The theory and practice of hygiene (Notter and Firth). : Revised and largely re-written / by R.H. Firth.

  • James Lane-Notter
Date:
1908
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Licence: In copyright

Credit: The theory and practice of hygiene (Notter and Firth). : Revised and largely re-written / by R.H. Firth. Source: Wellcome Collection.

Provider: This material has been provided by London School of Hygiene & Tropical Medicine Library & Archives Service. The original may be consulted at London School of Hygiene & Tropical Medicine Library & Archives Service.

    1045/1080 (page 981)
    APPENDIX 9gl peel from the ends is cut off, and the wedges so obtained allowed to soak over nioht in cold water to get rid of any excess of starch. Each wedge ot potato is then placed in a test-tube previously fitted with a pad of cotton- wool at the bottom, and filled for about half an inch in depth with distilled water. The tube is now plugged with cotton-wool, and sterilised at 100 U for twenty minutes on three successive days. Drigalski-Conradi Medium. (1) Agar preparation—To 3 lb. of finely cut beef add 2 litres of water ; allow the mixture to stand until next day. Boil the expressed meat-juice for one hour and filter ; add 20 grammes of Witte's peptone, 20 grammes of nutrose, 10 grammes of sodium chloride, and boil the whole again for an hour and then filter. Now add 70 grammes of agar, boil for three hours, render slightly alkaline to litmus, filter and boil for half an hour. (2) Litmus solution—Take 260 c.c. of either Kubel and Tiemann's litmus solution, or of a purified litmus solution, prepared as ex- plained later ; boil for ten minutes ; add 30 grammes of lactose and boil for fifteen minutes. Add this hot litmus-lactose solution to the liquid-agar solution and mix ; render it faintly alkaline ; then add 4 c.c. of a hot sterile solution of 10 per cent, water-free soda and 20 c.c. of a freshly prepared solution of 0-1 gramme crystal violet (Hochst) in 100 c.c. of warm sterile distilled water. The result is a meat-water peptone nutrose agar, containing 13 per cent, litmus and 0-01 per 1000 crystal violet. Tube, and sterilise m steam for thirty minutes. Eyre * has suggested a modified nutrose agar which is equally satisfactory. Litmus Solution.—For bacteriological work a pure solution of the blue dye (azolitmin) should be used. It is freely soluble in water, but in- soluble in alcohol. It can be prepared as follows :—Digest 2 ounces of powdered litmus with fresh quantities of hot water until all the colouring- matter is dissolved out; allow to settle and decant off the fluid. Evaporate this solution down from about a litre to 300 c.c. ; add a slight excess of acetic acid ; evaporate further over a water-bath until the liquid becomes pasty. Add 200 c.c. of methylated spirit and mix. The spirit precipitates the azolitmin, leaving the red dye in solution. Filter. Wash out dish and filter with methylated spirit. Now dissolve the pure blue colouring-matter on the filter in warm distilled water and dilute to 500 c.c. This azolitmin solution is far more sensitive than ordinary litmus solution. Neutral-red Bile-salt Agar.—Dissolve 20 grammes of agar m a litre of water in an autoclave ; add 5 grammes of sodium taurocholate and 20 grammes of peptone. Clear by means of white of egg in usual way and filter. Now add 10 grammes of lactose and 5 c.c. of a 1 per cent, solution of neutral red. Tube and sterilise for twenty minutes on two successive days. It is best to have the neutral-red solution freshly prepared. Endo's Fuchsin-agar.—To 1 litre of water add 500 grammes of minced beef, 10 grammes of peptone, 5 grammes of sodium chloride, and 30 grammes of agar. Boil well, filter, and neutralise; then make alkaline by adding 10 c.c. of a 10 per cent, solution of sodium carbonate. Now add 10 grammes of lactose, and 5 c.c. of a 10 per cent, fuchsin solution in 96 per cent, of alcohol. The medium is now a dark red colour. Twenty-five c.c. of a 10 per cent, sodium sulphite solution are now added. The medium gradually decolorises. Tube and sterilise once for half an hour in steam. On this medium, colonies of B. CoU are red, those of B. typhosus are colourless and transparent. The finished medium should be kept in the dark, other- wise it turns red. Gachtgens has suggested a modification of this medium by adding 033 per cent, of caffein and giving it an alkalinity equal to * Eyro : Trans. I'alholog. Hoc. London, vol. lv. ]>. 91.